Method of controlling operating clock frequency of hard disk drive, recording medium, and hard disk drive

CROSS-REFERENCE TO RELATED APPLICATIONS

p-0002This application claims priority under 35 U.S.C. §119 from Korean Patent Application No. 10-2006-0037708, filed on Apr. 26, 2006, the disclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

p-00031. Field of the Invention

p-0004The present general inventive concept relates to a system to control an operating clock frequency of a hard disk drive, and more particularly, to a method of adaptively controlling an operating clock frequency of a hard disk drive according to an operating environment of the hard disk drive by analyzing a command workload, a recording medium to record the method, and a hard disk drive using the method.

p-00052. Description of the Related Art

p-0006Performance of hard disk drives increases in proportion to an operating clock frequency. However, when the operating clock frequency is increased to increase the performance of a hard disk drive, power consumption of the hard disk drive is also increased.

p-0007A low operating clock frequency is usually used in mobile drives to decrease power consumption. However, high performance of a drive may be required depending on an environment in which the drive is used. In some instances, low power consumption may be more desirable than high performance. For example, when a quantity of command workload is large like in a compiling or rendering operation, the high performance of a hard disk drive is required, and therefore, the hard disk drive needs to be operated at a high operating clock frequency. On the other hand, when the hard disk drive is used to see movies, the low power consumption takes precedence over the performance, and therefore, the hard disk drive needs to be operated at the low operating clock frequency.

p-0008A command workload indicates a total number of write/read commands received by a hard disk drive during a predetermined reference time. Accordingly, when an amount of operation increases in the hard disk drive, the command workload also increases.

p-0009As described above, priority between high performance and low power consumption in a hard disk drive may change according to an operating environment of the hard disk drive. Accordingly, when the operating clock frequency of the hard disk drive is fixed, the hard disk drive cannot be used efficiently in various operating environments.

SUMMARY OF THE INVENTION

p-0010The present general inventive concept provides a method of controlling an operating clock frequency of a hard disk drive based on a result of analyzing a command workload to adaptively operate the hard disk drive according to an operating environment, a recording medium to record the method, and a hard disk drive using the method.

p-0011Additional aspects and advantages of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept.

p-0012The foregoing and/or other aspects of the present general inventive concept may be achieved by providing a method of controlling an operating clock frequency of a hard disk drive, the method including a command workload analyzing operation and an operating clock frequency changing operation.

p-0013In a command workload analyzing operation, a total number of write/read commands received during a predetermined reference time may be analyzed (or counted). In the operating clock frequency changing operation, the operating clock frequency of the hard disk drive may be changed or maintained based on an analysis result. The command workload may be compared with at least one reference value, and a mode corresponding to a comparison result may be set.

p-0014When a mode set in advance is different from the mode currently set based on the comparison result, an operating clock frequency corresponding to the mode set in advance may be changed into a second operating clock frequency corresponding to the currently set mode. When the operating clock frequency of the hard disk drive is changed, at least one external interrupt may be disabled until the operating clock frequency of the hard disk drive is changed completely.

p-0015The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing a method of controlling an operating clock frequency of a hard disk drive, the method including a time measuring operation and an operating clock frequency changing operation.

p-0016In the time measuring operation, a time taken to receive a predetermined number of write/read commands may be measured. In the operating clock frequency changing operation, the measured time may be compared with at least one reference value and a mode based on the comparison result may be set. When a mode set in advance is different from the mode currently set based on the comparison result, an operating clock frequency corresponding to the mode set in advance is changed into a second operating clock frequency corresponding to the currently set mode.

p-0017The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing a method of controlling an operating clock frequency of a hard disk drive, the method including changing an operating clock frequency of a hard disk drive to another operating clock frequency according to at least one of a command workload, a mode to operate the hard disk drive, and a time taken to receive one or more commands.

p-0018The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing a computer-readable recording medium having embodied thereon a computer program to execute a method of controlling an operating clock frequency of a hard disk drive, the method including analyzing a command workload, and changing an operating clock frequency of a hard disk drive according to the analyzed command workload.

p-0019The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing a computer-readable recording medium having embodied thereon a computer program to execute a method of controlling an operating clock frequency of a hard disk drive, the method including generating a command workload, comparing the command workload with at least one reference value and setting a mode according to the comparison, and when a mode set in advance is different from the mode currently set according to the comparison, changing an operating clock frequency corresponding to the mode set in advance into a second operating clock frequency corresponding to the currently set mode.

p-0020The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing a computer-readable recording medium having embodied thereon a computer program to execute a method of controlling an operating clock frequency of a hard disk drive, the method including measuring a time taken to receive a predetermined number of write/read commands, comparing the measured time with at least one reference value and setting a mode based on a comparison result, and when a mode set in advance is different from a mode currently set based on the comparison result, changing an operating clock frequency corresponding to the mode set in advance into a second operating clock frequency corresponding to the currently set mode.

p-0021The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing a computer-readable recording medium having embodied thereon a computer program to execute a method of controlling an operating clock frequency of a hard disk drive, the method including changing an operating clock frequency of a hard disk drive to another operating clock frequency according to at least one of a command workload, a mode to operate the hard disk drive, and a time taken to receive one or more commands.

p-0022The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing a hard disk drive including a host interface unit and an operating clock frequency control block. The hard disk drive communicates with a host through the host interface unit.

p-0023The operating clock frequency control block may analyze a command workload based on at least one command input through the host interface unit, may control an operating clock frequency of the hard disk drive based on an analysis result, and may output a controlled operating clock frequency.

p-0024The operating clock frequency control block may set a mode based on a result of a comparison of the analyzed command workload with at least one reference value. Alternatively, the operating clock frequency control block may measure a time taken to receive a predetermined number of write/read commands, compare the measured time with at least one reference value, and set the mode corresponding to the comparison result.

p-0025When a mode set in advance is different from the mode currently set based on the comparison result, the operating clock frequency control block may change an operating clock frequency corresponding to the mode set in advance into a second operating clock frequency corresponding to the currently set mode.

p-0026The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing a hard disk drive including an operating clock frequency control unit to change an operating clock frequency of a hard disk drive to another operating clock frequency according to at least one of a command workload, a mode to operate the hard disk drive, and a time taken to receive one or more commands.

BRIEF DESCRIPTION OF THE DRAWINGS

p-0027These and/or other aspects and advantages of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

p-0028<figref idrefs="DRAWINGS">FIG. 1</figref> is a flowchart illustrating a method of controlling an operating clock frequency of a hard disk drive according to an embodiment of the present general inventive concept;

p-0029<figref idrefs="DRAWINGS">FIG. 2</figref> is a flowchart illustrating a method of controlling an operating clock frequency of a hard disk drive according to another embodiment of the present general inventive concept;

p-0030<figref idrefs="DRAWINGS">FIG. 3</figref> is a flowchart illustrating a procedure to change an operating clock frequency in accordance with a current mode, according to an embodiment of the present general inventive concept; and

p-0031<figref idrefs="DRAWINGS">FIG. 4</figref> illustrates a block diagram illustrating a hard disk drive to control an operating clock frequency according to an embodiment of the present general inventive concept.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

p-0032Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures.

p-0033<figref idrefs="DRAWINGS">FIG. 1</figref> is a flowchart illustrating a method of controlling an operating clock frequency of a hard disk drive according to an embodiment of the present general inventive concept. In operation S<b>110</b>, a first clock frequency f<b>1</b> and a reference time t<b>1</b> are set in the hard disk drive. Information on the first clock frequency f<b>1</b> and the reference time t<b>1</b> may be stored in a predetermined data storage unit (for example, a register) within the hard disk drive or may be stored in software. In this case, the hard disk drive operates at the first clock frequency f<b>1</b>. The reference time t<b>1</b> may be set in a predetermined time unit, for example, 30 seconds or 1 minute. Expiration of the reference time t<b>1</b> may be checked using a timer.

p-0034In operation S<b>120</b>, the hard disk drive receives a command from a host, e.g., a personal computer (PC). In operation S<b>130</b>, the hard disk drive determines whether the command is a write command or a read command. When the command is the write command or the read command, the hard disk drive counts the command as one of a number of input commands, i.e., a command count “n” in operation S<b>140</b>. If the command is neither the write command nor the read command, the hard disk drive does not count the command.

p-0035If it is determined that the reference time t<b>1</b> has not expired in operation S<b>150</b>, operations S<b>120</b> and S<b>130</b> or operations S<b>120</b>, S<b>130</b>, and S<b>140</b> are repeated. A time taken from the receipt of the write or read command is compared with the reference time t<b>1</b> so as to determine whether the reference time t<b>1</b> is expired. If it is determined that the reference time t<b>1</b> has expired in operation S<b>150</b>, the hard disk drive compares the command count “n” with a first reference value X<b>1</b> in operation S<b>160</b>.

p-0036When the command count “n” is greater than the first reference value X<b>1</b>, i.e., n>X<b>1</b>, an operating clock frequency of the hard disk drive is set at a third operating clock frequency CLK<b>3</b>, and a third mode is set (or referred to as “a third mode”), in operation S<b>161</b>. Thus, the first clock frequency f<b>1</b> is changed to the third operating clock frequency CLK<b>3</b> in operation S<b>180</b>. When the command count “n” is greater than the first reference value X<b>1</b> during the reference time t<b>1</b>, the hard disk drive has been in an operating environment requiring frequent data input/output. Accordingly, the hard disk drive will be operated at a high operating clock frequency, i.e., the third operating clock frequency CLK<b>3</b> to increase a performance thereof. Therefore, operation S<b>160</b> may be performed after the operation S<b>140</b> and before operation S<b>150</b> to determine whether the command count “n” is greater than the first reference value x<b>1</b>. If n>x<b>1</b>, S<b>161</b> is performed. If n<x<b>1</b>, S<b>150</b> is performed. The operations S<b>160</b> and S<b>161</b> may be performed when it is determined that t<t<b>1</b> in operation S<b>150</b>.

p-0037When the command count “n” is less than or equal to the first reference value X<b>1</b> and is greater than a second reference value X<b>2</b>, i.e., X<b>2</b>&lt;n≦X<b>1</b> in operation S<b>170</b>, the operating clock frequency of the hard disk drive is set at a second operating clock frequency CLK<b>2</b> (where CLK<b>2</b>&lt;CLK<b>3</b>) and a second mode is set (or referred to as “a second mode”), in operation S<b>171</b>. When the command count “n” is less than or equal to the first reference value X<b>1</b> and is greater than the second reference value X<b>2</b>, the hard disk drive will be operated at the second operating clock frequency CLK<b>2</b> which is proper in terms of both performance and power consumption. The second operating clock frequency CLK<b>2</b> may correspond to the first clock frequency f<b>1</b> (i.e., CLK<b>2</b>=f<b>1</b>) and may be a default operating clock frequency.

p-0038When the command count “n” is less than or equal to the second reference value X<b>2</b>, i.e., n≦X<b>2</b> in operation S<b>170</b>, the operating clock frequency of the hard disk drive is set at a first operating clock frequency CLK<b>1</b> (where CLK<b>1</b>&lt;CLK<b>2</b>) and a first mode is set (or referred to as “a first mode”), in operation S<b>172</b>. When the command count “n” is less than or equal to the second reference value X<b>2</b>, the hard disk drive has been in an operating environment requiring a small number of data inputs/outputs. Accordingly, the hard disk drive will be operated at the first operating clock frequency CLK<b>1</b> to decrease a power consumption thereof.

p-0039In operation S<b>180</b>, the operating clock frequency of the hard disk drive is changed into an operating clock frequency (e.g., the first operating clock frequency CLK<b>1</b>) corresponding to a mode (e.g., the first mode) set through operations S<b>160</b>, S<b>161</b>, S<b>170</b>, S<b>171</b>, and S<b>172</b>. After the change or a non-change of the operating clock frequency is completed, the command count “n” is reset in operation S<b>181</b> and a timer is reset in operation S<b>182</b>.

p-0040<figref idrefs="DRAWINGS">FIG. 2</figref> is a flowchart illustrating a method of controlling an operating clock frequency of a hard disk drive according to another embodiment of the present general inventive concept. In operation S<b>210</b>, a first clock frequency f<b>1</b> and a reference command count K<b>1</b> are set in the hard disk drive. Then, the hard disk drive operates at a first clock frequency f<b>1</b>. The reference command count K<b>1</b> may be set in a predetermined count unit, for example, K<b>1</b> may be set to be equal to 1000. Whether the reference command count K<b>1</b> is exceeded may be checked using a predetermined command counter.

p-0041In operation S<b>220</b>, the hard disk drive receives a command from a host, e.g., a PC. In operation S<b>230</b>, the hard disk drive determines whether the command is a write command or a read command. When the command is the write command or the read command, the hard disk drive counts the command as a number of input commands, i.e., a command count “n” in operation S<b>240</b>. If the command is neither the write command nor the read command, the hard disk drive does not count the command.

p-0042If it is determined that the command count “n” does not exceed a reference command count K<b>1</b> in operation S<b>250</b>, operations S<b>220</b>, S<b>230</b>, and S<b>240</b> are repeated and a time “t” taken until the command count “n” exceeds the reference command count K<b>1</b> is measured. The time “t” may be measured using a timer.

p-0043If it is determined that the command count “n” exceeds the reference command count K<b>1</b>, i.e., n>K<b>1</b> in operation S<b>250</b>, the time “t” taken to reach the command count “n” is compared with a first reference value t<b>1</b> in operation S<b>260</b>.

p-0044When the time “t” is greater than the first reference value t<b>1</b>, i.e., t>t<b>1</b>, the operating clock frequency of the hard disk drive is set at a first operating clock frequency CLK<b>1</b> and a first mode is set (or referred to as “a first mode”), in operation S<b>261</b>. When the time “t” taken to receive as many write/read commands as the reference command count K<b>1</b> is greater than the first reference value t<b>1</b>, the hard disk drive has been in an operating environment requiring a small number of data inputs/outputs. Accordingly, the hard disk drive will be operated at the first operating clock frequency CLK<b>1</b> to decrease a power consumption thereof.

p-0045When the time “t” taken to receive as many write/read commands as the reference command count K<b>1</b> is less than or equal to the first reference value t<b>1</b> and is greater than a second reference value t<b>2</b>, i.e., t<b>2</b>&lt;t≦t<b>1</b> in operation S<b>270</b>, the operating clock frequency of the hard disk drive is set at a second operating clock frequency CLK<b>2</b> (where CLK<b>1</b>&lt;CLK<b>2</b>) and a second mode is set (or referred to as “a second mode”), in operation S<b>271</b>. When the time “t” is less than or equal to the first reference value t<b>1</b> and is greater than the second reference value t<b>2</b>, the hard disk drive will be operated at the second operating clock frequency CLK<b>2</b> which is proper in terms of both performance and power consumption. The second operating clock frequency CLK<b>2</b> may correspond to the first clock frequency f<b>1</b> (i.e., CLK<b>2</b>=f<b>1</b>) and may be a default operating clock frequency.

p-0046When the time “t” taken to receive as many write/read commands as the reference command count K<b>1</b> is less than or equal to the second reference value t<b>2</b>, i.e., t≦t<b>2</b> in operation S<b>270</b>, the operating clock frequency of the hard disk drive is set at a third operating clock frequency CLK<b>3</b> (where CLK<b>2</b>&lt;CLK<b>3</b>) and a third mode is set (or referred to as “a third mode”), in operation S<b>272</b>. When the time “t” is less than or equal to the second reference value t<b>2</b>, the hard disk drive has been in an operating environment requiring frequent data input/output. Accordingly, the hard disk drive will be operated at a high operating clock frequency, i.e., the third operating clock frequency CLK<b>3</b> to increase a performance thereof.

p-0047In operation S<b>280</b>, the operating clock frequency of the hard disk drive is changed into an operating clock frequency (e.g., the first operating clock frequency CLK<b>1</b>) corresponding to a mode (e.g., the first mode) set through operations S<b>260</b>, S<b>261</b>, S<b>270</b>, S<b>271</b>, and S<b>272</b>. After the change or a non-change of the operating clock frequency is completed, the command count “n” is initialized in operation S<b>281</b> and a timer is initialized in operation S<b>282</b>.

p-0048<figref idrefs="DRAWINGS">FIG. 3</figref> is a flowchart illustrating a method to change an operating clock frequency of a current mode of a hard disk drive, according to an embodiment of the present general inventive concept. Referring to <figref idrefs="DRAWINGS">FIGS. 1</figref>, <b>2</b>, and <b>3</b>, a mode (specifically a signal-indicating the mode, e.g., a first mode) set in the method illustrated in <figref idrefs="DRAWINGS">FIG. 1</figref> or <b>2</b> is received in operation S<b>310</b>. The hard disk drive compares the current mode or the signal indicating the current mode (e.g., a second mode), which has been set in advance, with a received mode or a signal indicating the received mode (e.g., the first mode) in operation S<b>320</b>. The received mode may be transmitted from a PC or a memory device.

p-0049When the current mode is not the same as the received mode, the hard disk drive disables an external interrupt in operation S<b>330</b> if there is any external interrupt.

p-0050In operation S<b>340</b>, an operating clock frequency (e.g., CLK<b>2</b>) corresponding to the current mode (e.g., the second mode) is changed into an operating clock frequency (e.g., CLK<b>1</b>) corresponding to the received mode (e.g., the first mode). In operation S<b>350</b>, after the change of the operating clock frequency is completed, the external interrupt is enabled. In operation S<b>360</b>, the hard disk drive operates in response to the changed-operating clock frequency (CLK<b>1</b>). For example, when the current mode is the second mode and the received mode is a third mode, the external interrupt is disabled and a second operating clock frequency CLK<b>2</b> of the hard disk drive is changed into a third operating clock frequency CLK<b>3</b> corresponding to the third mode.

p-0051When the current mode is the same as the received mode, the operating clock frequency of the hard disk drive is not changed in operation S<b>360</b>.

p-0052<figref idrefs="DRAWINGS">FIG. 4</figref> is a block diagram illustrating a hard disk drive <b>400</b> to control an operating clock frequency according to an embodiment of the present general inventive concept. The hard disk drive <b>400</b> includes constituent elements, such as a host interface unit <b>410</b> and an operating clock frequency control block <b>420</b>.

p-0053The hard disk drive <b>400</b> communicates with a host through the host interface unit <b>410</b>. The operating clock frequency control block <b>420</b> analyzes (or counts) a command workload based on at least one command COM (e.g., a write command or a read command) input through the host interface unit <b>410</b>, controls (e.g., changes or maintains) an operating clock frequency of the hard disk drive based on an analysis (or a counting) result, and outputs a controlled operating clock frequency. The controlled operating clock frequency may be provided to a predetermined internal circuit operating in response to the operating clock frequency.

p-0054Although not illustrated in <figref idrefs="DRAWINGS">FIG. 4</figref>, other constituent elements of the hard disk drive, such as a plurality of disks, a plurality of heads, a preamplifier, a actuator, a read/write channel circuit, a spindle motor, a spindle motor driver, a voice coil motor, a voice coil motor driver, etc., are in general common and known to one of ordinary skill in the art of hard disk drives. Thus, detailed descriptions thereof will be omitted.

p-0055The operating clock frequency control block <b>420</b> compares a result of analyzing the command workload with at least one reference value and sets a mode corresponding to a comparison result. If a mode that has been set in advance is different from the mode set based on the comparison result, the operating clock frequency control block <b>420</b> changes an operating clock frequency corresponding to the mode set in advance into an operating clock frequency corresponding to a currently set mode. When an external interrupt is input, the operating clock frequency control block <b>420</b> disables the external interrupt before changing the operating clock frequency of the hard disk drive.

p-0056The operating clock frequency control block <b>420</b> may include a data storage device <b>421</b> and a controller <b>422</b>. A program to set the operating clock frequency of the hard disk drive is recorded in the data storage device <b>421</b>. The data storage device <b>421</b> may be implemented as a read-only memory (ROM) device or a flash memory device, but the present general inventive concept is not restricted thereto.

p-0057The data storage device <b>421</b> generates a predetermined signal T in response to a predetermined command RCOM output from the controller <b>422</b>. The controller <b>422</b> executes a program to set the operating clock frequency, which is stored in the data storage device <b>421</b>, in response to the predetermined signal T output from the data storage device <b>421</b> so that the operating clock frequency of the hard disk drive is changed.

p-0058For example, when there is not an external interrupt and the hard disk drive is operating at a first clock frequency (e.g., f<b>1</b>=CLK<b>2</b>), the first clock frequency CLK<b>2</b> may be a default value set by the program.

p-0059When a result of counting write/read commands output from the host during a predetermined reference time is greater than a first reference value, the controller <b>422</b> changes the first clock frequency CLK<b>2</b> into a third operating clock frequency CLK<b>3</b>. When the counting result is less than or equal to a second reference value, the controller <b>422</b> changes the first clock frequency CLK<b>2</b> into a first operating clock frequency CLK<b>1</b>. When the counting result is less than or equal to the first reference value and is greater than the second reference value, the controller <b>422</b> may not change the first clock frequency CLK<b>2</b>.

p-0060Alternatively, the operating clock frequency control block <b>420</b> may control the operating clock frequency of the hard disk drive as follows.

p-0061The operating clock frequency control block <b>420</b> measures a time taken to receive a predetermined number of write/read commands through the host interface unit <b>410</b>, compares the measured time with at least one reference value, sets a mode corresponding to a comparison result, and if the mode that has been set in advance is different from the mode currently set based on the comparison result, and changes the operating clock frequency corresponding to the mode set in advance into the operating clock frequency corresponding to the currently set mode.

p-0062For example, the controller <b>422</b> included in the operating clock frequency control block <b>420</b> counts at least one of a write command or a read command received from the host and measures a time taken until a counted number reaches a predetermined reference command count. It is assumed that the hard disk drive is operating at the first clock frequency CLK<b>2</b> corresponding to a second mode.

p-0063When the measured time is greater than the first reference value, the first clock frequency CLK<b>2</b> is changed to the first operating clock frequency CLK<b>1</b> (CLK<b>1</b>&lt;CLK<b>2</b>) corresponding to a first mode of the hard disk drive. When the measured time is greater than the first reference value, the hard disk drive has been in an operating environment requiring a small number of data inputs/outputs. Accordingly, the operating clock frequency control block <b>420</b> changes the operating clock frequency of the hard disk drive to a low clock frequency, i.e., the first operating clock frequency CLK<b>1</b>, to decrease a power consumption of the hard disk drive.

p-0064The data storage device <b>421</b> and the controller <b>422</b> in the operating clock frequency control block <b>420</b> may operate in association with each other to control the operating clock frequency of the hard disk drive, but the present general inventive concept is not restricted thereto.

p-0065The above-described methods of controlling an operating clock frequency of a hard disk drive, can also be embodied as computer readable program codes on a computer readable recording medium. The computer readable recording medium is any data storage device that can store data which can be thereafter read by a computer system. Examples of the computer readable recording medium include read-only memory (ROM), flash memory, random-access memory (RAM), CD-ROMs, magnetic tapes, optical data storage devices, and carrier waves (such as data transmission through the internet).

p-0066The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. Also, functional programs, codes, and code segments to accomplish the present general inventive concept can be easily construed by programmers skilled in the art to which the present general inventive concept pertains. The methods illustrated in <figref idrefs="DRAWINGS">FIGS. 1</figref>, <b>2</b>, and <b>3</b> can be stored in the computer-recorded medium in a form of computer-readable codes to perform the method when the computer reads the computer-readable codes of the recording medium.

p-0067As described above, according to the present general inventive concept, an operating clock frequency of a hard disk drive is controlled based on a result of analyzing a command workload which changes according to an operating environment of the hard disk drive so that a performance of the hard disk drive is improved or a power consumption thereof is reduced.

p-0068Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.